The anticoagulant citrate is a small molecule frequently used in medical procedures, especially those involving blood collection and processing like apheresis or blood transfusions. Citrate ensures that blood remains fluid outside the body, preventing it from clotting inside collection bags or medical tubing. This is particularly important in apheresis, where a patient’s or donor’s blood is temporarily circulated through a machine to separate specific components, such as platelets or plasma, before returning the remaining blood. The body’s efficient metabolic machinery rapidly processes the citrate.
Citrate’s Role in Stopping Coagulation
Citrate prevents blood from clotting by interacting chemically with a specific mineral. Blood coagulation relies on a complex chain reaction involving clotting factors, which require ionized calcium to activate. Citrate functions as a chelating agent, binding tightly to circulating ionized calcium and other divalent cations like magnesium.
By sequestering the free calcium, citrate removes this necessary component from the blood. This action interrupts the coagulation cascade, preventing the formation of fibrin and stopping the blood from clotting. Since the binding is reversible, the blood’s ability to clot is only suppressed while citrate is present and bound to the calcium.
How the Body Processes Citrate
The metabolism of infused citrate is swift in a healthy individual. The body recognizes citrate as a natural substance because it is an intermediate compound in the body’s primary energy generation pathway, known as the Krebs cycle. Clearance occurs mainly in the liver, with the kidneys and skeletal muscles contributing to a lesser extent.
Within the mitochondria of these cells, the infused citrate is rapidly converted into carbon dioxide and water. This metabolic process consumes hydrogen ions, resulting in the production of bicarbonate. The production of bicarbonate explains why citrate solutions can have an alkalizing effect on the blood.
The typical half-life of citrate in the circulation of a healthy person is extremely short, generally ranging from 30 to 60 minutes, though it can be as quick as five minutes under certain conditions. This rapid processing ensures that the anticoagulant effect is quickly reversed once the infusion is stopped. However, individuals with liver impairment may clear citrate at a significantly slower rate, sometimes requiring adjustments to the procedure or monitoring.
Temporary Effects of Rapid Citrate Infusion
Rapid infusion of citrate during procedures like apheresis can temporarily overwhelm the system’s ability to metabolize it. This temporary imbalance leads to an acute, mild reduction in the concentration of ionized calcium in the bloodstream. This transient drop in calcium causes symptoms because calcium is necessary for proper nerve and muscle function.
The most common temporary effects are neurological, characterized by a tingling sensation, or paresthesia, often felt around the mouth and in the extremities. Other mild symptoms include shivering, light-headedness, or mild nausea. These effects are generally short-lived, resolving quickly once the citrate concentration in the blood begins to decrease.
Medical staff closely monitor for these signs. If symptoms are noticeable, the rate of citrate infusion may be slowed down to allow the liver to catch up with the metabolism. If symptoms persist, calcium supplementation, usually oral or intravenous, may be administered to quickly restore ionized calcium levels and alleviate discomfort.